1. Field of the Invention
The present invention relates to a recording and simultaneous verifying method of a phase-changing type off information recording medium in which this method is utilized in fields of devices relative to an optical memory, etc., and information can be recorded, regenerated and rewritten by changing a phase of the material of a recording layer by irradiating an optical beam onto the information recording medium.
2. Description of the Related Art
A so-called phase-changing type of information recording medium is well known as one of optical memory media in which information can be recorded, regenerated and erased by irradiating an electromagnetic wave, especially, a laser beam to this recording medium. This phase-changing type of information recording medium uses a transition between a crystal phase and a noncrystal phase, or a transition between crystal phases. It is difficult to overwrite information by a single beam in the case of a magneto-optic memory. However, in accordance with this phase-changing type of information recording medium, information can be especially overwritten by a single beam. Further, the construction of an optical system on a driving side of the phase-changing type of information recording medium is simplified in comparison with the magneto-optic memory. Therefore, the phase-changing type of information recording medium has recently been searched and developed actively.
For example, U.S. Pat. No. 3,530,441 shows a typical example of such a phase-changing type of information recording medium. In this United States Patent, the phase-changing type of information recording medium uses a so-called chalcogen alloy material such as Ge-Te, Ge-Te-Sn, Ge-Te-S, Ge-Se-S, Ge-Se-Sb, Ge-As-Se, In-Te, Se-Te, Se-As, etc. In Japanese Patent Application Laying Open (KOKAI) No. 61-219692, gold (Au) is added to a Ge-Te including material to improve stability of the recording medium and crystallize the recording medium at a high speed, etc. In Japanese Patent Application Laying Open (KOKAI) No. 61-270190, tin (Sn) and gold (Au) are added to the chalcogen alloy material. In Japanese Patent Application Laying Open (KOKAI) No. 62-19490, palladium (Pd) is added to the chalcogen alloy material. Further, in Japanese Patent Application Laying Open (KOKAI) No. 62-73438, a composition ratio of Ge-Te-Se-Sb and Ge-Te-Sb in the chalcogen alloy material is specified to improve cyclability of data recording and erasing operations.
However, all recording characteristics required for the phase-changing type of information recording medium are not satisfied in each of these publications. In particular, the most important subjects to be solved are to prevent an erasing ratio of data from being reduced by an incomplete erasing operation at an overwriting, and to increase the number off cyclability of overwriting.
Japanese Patent Application Laying Open (KOKAI) No. 63-251290 proposes a phase-changing type of information recording medium having a recording layer composed of a single phase off compound whose crystal state is substantially equal to a ternary compound or more. In this kind of recording layer, a ternary compound such as In.sub.3 SbTe.sub.2, etc. having a stoichiometric composition exists at a ratio of 90 molecular percent (%) or more. By using such a recording layer, recording and erasing characteristics of the recording medium is improved. However, an erasure ratio still remains low.
In consideration of these situations, it is desirable to develop a phase-changing type of information recording medium having a high data erasure ratio and an excellent cyclability.
Materials for a protective layer suitable for a material of the recording layer have been also developed. For example, ZnSSiO.sub.2, Al.sub.2 O.sub.3, Ta.sub.2 O.sub.5, SiN, AlN, etc. are used as the protective layer. However, all characteristics of the recording medium required for an optical memory medium are not satisfied at present even with these materials.
Generally, in the magneto-optic memory, it is necessary to perform three operations composed of erasing, recording and verifying data. In this case, accordingly, three rotations of the disk are required. Therefore, a data writing speed is apparently low in comparison with a magnetic disk that requires two operations composed of recording and verifying data. In this case, which is represented by hard disk, two rotations or less of the disk are normally required. For the phase-changing type of information recording medium, two operations composed of recording and verifying are also required with existing technology. This is a great obstacle to a reduction of the data writing speed. Concretely, the data writing speed is two or three times slower than that in the magnetic disk, which leads to a low data transfer rate.